The present invention relates generally to medical devices and, more particularly, to a central venous catheter having a multilumen soft tip whose flexibility is not compromised when a medical implement is located in one of the lumens of the soft tip during the use of the catheter. Even more specifically, the above-mentioned medical implement is fiber optics for measuring oxygen saturation of blood.
Central venous (CV) catheters are used primarily to gain access to the venous vasculature for fluid infusion, blood sampling and central venous pressure monitoring. CV catheters are inserted into the patient using the Seldinger technique. This involves identifying the target vein, puncturing the vein and inserting a guidewire. A vessel dilator is inserted over the guidewire and pushed through the vessel wall to create an opening for the CV catheter. The dilator is removed though the guidewire remains in place. The single lumen CV catheter is then threaded over the guidewire and pushed through the tissue and into the vessel. Importantly, the catheter is inserted without any stiffening members other than the guidewire. The tissue and vessel wall resist the catheter as it slides into the vessel. Therefore, to insure the catheter can easily slide into the body, the catheter body and catheter tip must be sufficiently rigid to slide over the guidewire into the blood vessel without buckling or otherwise collapsing. More than one lumen in the distal tip creates an asymmetry in the transverse cross-section and increases the chances of buckling. Therefore, CV catheters are uniformly constructed with a single lumen at the distal tip. Of course, any catheters that require such a soft tip are at present single lumen, not just CV catheters.
Once a CV catheter is placed into the blood vessel, then the stiffness that was desirable during insertion through the vessel wall becomes a disadvantage. Vessel perforation is always a concern in the design of these catheters. Another concern is that the catheter tip migrates from the central vena cava to the right atrium. The right atrium contains regions of thick and thin walls. During routine monitoring, if catheter has migrated into the right atrium, through the action of normal heart beats, and lodges into the heart wall in one of the thin walls sections, the catheter tip can punch through the atrial wall and create cardiac tamponade. If the superior vena cava above the pericardial sac is perforated, a pleural infusion is created, leaking fluid into the pleural or lung cavity. During use, a stiff catheter and tip increases the possibility of endothelial abrasion and vessel wall or right atrium wall perforation. Such perforation generally requires surgical intervention to resolve.
Because of these dangers, CV catheters typically include a soft distal tip that yields when it contacts a vessel wall, and a radiopaque marker is incorporated into the tip to monitor its location within the body. This reduces, but does not eliminate, the possibility of the catheter perforating the vessel wall during repeated contact during use. Therefore, CV catheters tips have been made with softer materials to yield more easily when contacting a vessel wall. Such tips are made of materials such as low durometer urethanes, for example Tecoflex and Pellethane, due to their high durability and ease of manufacturing. Importantly, however, all commercially available CV catheters with soft distal tips have one common feature—their distal tip has only a single lumen which is used for passing a guidewire during insertion and later during the use of the catheter may serve for fluid infusion. Such a lumen extending through the distal tip does not have any medical implement, for example, a sensor or a probe, located within because it would compromise the flexibility of the soft tip and would also interfere with the passing of the guidewire during insertion.
Pulmonary artery (PA) catheters, on the other hand, have blunt rigid tips because they are inserted through a vascular access introducer. Such an introducer has already been positioned within the target vessel, and includes a large bore port through which the PA catheter can be passed, and a hemostasis valve on its proximal end to prevent blood leakage around the catheter. Furthermore, many PA catheters require a stiff blunt tip to interface more efficiently with an in vitro calibrating device. Moreover, such stiff, flat tips are relatively easy to manufacture and facilitate polishing of the distal end of the optical fibers. Therefore, typically there is no need for a soft, tapered distal end on PA catheters. Consequently, rigid tipped catheters may include multiple lumens in their distal tips.
Mixed venous oxygen saturation (SvO2) is the amount of oxygen in blood taken from a vessel coming from the right side of the heart going into the lungs. This reflects the amount of oxygen being delivered to the tissues during cardiac arrest and shock. Selective venous hypoxemia or low oxygen content, when compared to arterial blood, is characteristically seen during cardiac arrest and shock.
When oxygen delivery to the tissues is low, the SvO2 is low. When oxygen delivery to the tissues is high, the SvO2 is normal or high. This provides the physiological basis for using SvO2 as an indicator of response to therapy while treating a patient in cardiac arrest or shock. Intermittent SvO2 measurement can be predictive of outcome in cardiac patients and hemodynamically unstable trauma patients and medical patients.
Typically, SvO2 is drawn from a pulmonary artery (PA) catheter which is between 65–110 centimeters long and is placed into a vein that accesses the right side of the heart and then into the pulmonary artery. However, placement of a PA catheter is extremely difficult and can be impractical during cardiac arrest and severe shock due to low blood pressure.
The central venous system is located much closer to the skin and can be more easily accessed during shock and cardiac arrest. Thus, a number of studies have supported the substitution of central venous (right atrial or superior vena cava) oxygen saturation (ScvO2) for pulmonary artery blood oxygen saturation (SvO2) during spontaneous circulation, circulatory failure, and closed chest CPR. The central venous blood can be obtained much more easily than blood from the pulmonary artery under conditions of shock and cardiac arrest. Thus, it is more feasible to use the central venous system as it provides similar information.
Fiber optic technology has previously been utilized in measuring ScvO2. U.S. Pat. No. 5,315,995 to Rivers ('995), issued May 31, 1994, describes a fiber optic catheter and its efficacy for continuous measurement of central venous oxygen saturation. The catheter includes a catheter body having a fiber optic bundle disposed therein. In operation, this catheter is inserted into the subclavian vein or internal jugular vein with the aid of a catheter introducer or guide wire. The '995 patent, however, does not teach a soft multiple lumen tip at all and does not even address the issue of keeping the distal tip of the catheter soft and flexible during use despite the presence of a fiber optic bundle.
Currently, there is no answer to the problem of keeping a CV catheter tip flexible when multiple lumens are required at the distal tip, let alone when one or more of the lumens contains a medical implement. Accordingly, there is a need for an improved central venous catheter having a soft tip that has multiple lumens and can measure physiologic parameters without the need for multiple catheter insertions.